The most familiar organization for bubble memory operation employs a pattern of magnetically soft or high permeability elements, typically permalloy, formed on the (coated) surface of an epitaxial film in which bubble movement occurs. The elements respond to a magnetic drive field reorienting in the plane of the film to generate a changing magnetic pole pattern operative to move bubbles in the film in what is commonly called a "field-access" mode of operation.
Typically, the elements are formed in a pattern which defines a parallel arrangement of closed loops in which bubble patterns are recirculated in parallel, successive patterns of bubbles moving into information "exchange positions" as the drive field reorients. The elements also define an accessing channel which comes into close proximity with the recirculating loops. Each stage of the accessing channel is associated with a recirculating loop at an exchange position for selectively affecting an exchange of information therebetween. Information exchange is controlled by an electrical conductor which couples the exchange positions serially. When pulsed, the conductor produces a transfer or replication of information depending on the pattern of elements at each exchange position.
The type of organization just described is called a "major-minor" organization and is disclosed in U.S. Pat. No. 3,618,054 of P. I. Bonyhard, U. F. Gianola, and A. J. Perneski issued Nov. 2, 1971. The recirculating loops are called minor loops and function as permanent stores. The accessing channel is called the major channel and serves to move data from a selected address to read and write ports in the major channel.
U.S. Pat. No. 3,810,133 of A. H. Bobeck and I. Danylchuk issued May 7, 1974 discloses a pattern of elements and a conductor geometry which operate, in exchange positions between minor loops and a major channel, to replicate information. The replicator is operative in response to a sequence of a bubble stretching pulse and a bubble cutting pulse to produce an image of data advanced to the exchange positions either from the minor loops or the major channel. It is characteristic of such a replicator that the sequence of pulses occurs as the drive field reorients, the pulses occurring 180.degree. apart with respect to a drive field cycle. Consequently, the phase relationship between the stretch and cut pulses is a constraint on the operation of the memory and results in limitations in the margins of operation for the memory.
There are other limitations to the operation of bubble memories similarly related to the replicator. For example, when the presence of a bubble is detected by a magnetoresistive element, noise due to the replicate pulses, as well as to the drive field necessary for a replication operation, generate noise in the output signal resulting in the degradation of the signal and necessitating increased sophistication in the detection circuitry. To an extent, this "high noise" condition is alleviated by replicating and detecting on alternative cycles of the drive field, a procedure not inconsistent with the fact that the physical space occupied by the elements which define the minor loops dictates that exchange positions in practice be associated with alternative stages of the major channel. Thus, adjacent bits occupy alternate stages of the accessing channel during operation.
A considerable improvement as far as phasing constraints and signal-to-noise ratio, would be achieved if a static replicator existed. That is to say, a pattern of elements and an electrical conductor geometry operative in conjunction with that pattern to produce an image of data (i.e., in minor loops) and to transfer that data to a second (i.e., major) channel while the drive field is in a fixed orientation, would allow relaxed phasing tolerances, improved signal-to-noise ratio, and less expensive detection circuitry.